1. Field of the Invention
The present invention relates generally to devices and methods for removing thrombus and clot from blood vessels. More particularly, the invention relates to a percutaneous technique where clot and thrombus are dislodged from the blood vessel and collected in the distal end of an intravascular catheter.
Atherosclerosis is a leading cause of death and disability throughout the world. Atherosclerosis is caused by the deposit of fatty substances on the interior wall of a blood vessel, where it is referred to as atheroma or plaque. Such atheromas are found in the peripheral circulatory system as well as the coronary arteries where they can cause severe occlusion of the arterial lumen. Further occluding the blood vessels, clot and thrombus result from platelet aggregation on the irregular surfaces of the lumens caused by the atheroma and plaque. Occluded blood vessels can cause a variety of clinical manifestations, including myocardial infarction (heart attack), angina pectoris, stroke, intermittent claudication, and gangrene. When the blockage of blood flow becomes sufficiently serious, it is necessary to intervene and recanalyze the blood vessel.
Numerous techniques are employed for such recanalization. One of the most common surgical techniques is referred to as embolectomy, where a blood vessel is entered through a surgical incision and a device introduced to the blood vessel for removing the clot and thrombus. Most commonly, a balloon-tipped device (such as the Fogarty catheter) is introduced through a surgical incision and advanced to the location of the occlusion. The balloon is then inflated at a point beyond the clot and used to translate the obstructing material back to the point of incision. The obstructing material can then be removed by the surgeon. While such surgical techniques have been of enormous value, the need to expose a patient to surgery is always traumatic and best avoided when possible.
A variety of percutaneous methods are also utilized for recanalization of blood vessels. The most common of such techniques is referred to as balloon angioplasty, where a balloon-tipped catheter is non-surgically introduced to a blood vessel, typically through an introducing catheter. The balloon-tipped catheter is then advanced to the point of stenosis and inflated in order to dilate the blockage. Balloon angioplasty, thus, does not actually remove stenotic material from the blood vessel, but rather compresses it outwardly in order to increase the available lumen size in the blood vessel. Balloon angioplasty has also been of great value in treating atherosclerosis, but suffers from its own disadvantages. Foremost among these, regions of atheroma and plaque which have been dilated are often subject to rapid restenosis. Even more problematic, the material which has been compressed against the wall of a blood vessel will sometimes dislodge and cause an abrupt closure of the lumen. The latter event can be catastrophic. Thus, balloon angioplasty is indicated only in certain circumstances and is not always successful even when indicated.
Other percutaneous recanalization techniques have also been proposed. Laser angioplasty involves the use of laser energy to oblate stenosis within the blood vessel. Although laser angioplasty has the advantage that the stenotic material is vaporized and not available for restenosis, most laser techniques are limited in their ability to open broad passages within the blood vessels. Indeed, they are frequently used only as a preliminary treatment modality to open a blood vessel sufficiently to allow subsequent balloon angioplasty. Additionally, laser angioplasty, if not properly controlled, can penetrate a blood vessel wall leading to catastrophic results.
A third percutaneous approach has been the use of open-ended catheters to perform aspiration thromboembolectomy. Although relatively safe, the use of negative pressure to collect thrombus is successful only with relatively soft thrombus. In order to improve such aspiration techniques, it has been proposed to use various front-end cutting catheters where a rotating blade is advanced to sever thrombus which is thereafter collected by vacuum in the front end of a catheter. Such improvements enhance the effectiveness of the technique, but increase the danger of vessel penetration by an errant cutting blade.
For these reasons, it would be desirable to provide improved methods for removing clot and thrombus from the interior of blood vessels by percutaneous techniques. In particular, such techniques should provide for effective removal of recalcitrant obstructions with little or no likelihood of traumatizing the blood vessel.
2. Description of the Relevant Art
Embolectomy catheters comprising a flexible catheter body having an inflatable balloon at their distal end are described in U.S. Pat. Nos. 3,435,826; 4,561,439; 4,734,093; and 4,762,130. Such embolectomy catheters are generally surgically introduced so that clot and thrombus may be translated to an incision in the blood vessel from where they can be removed. Embolectomy catheters having wire coils at their distal end are described in U.S. Pat. Nos. 4,706,671, and 4,650,466. The catheter in the '671 patent may be introduced to a blood vessel in a collapsed condition through a needle to remove thrombus. U.S. Pat. Nos. 4,636,195; 4,610,662; and 4,573,966 describe vascular catheters which carry axially spaced-apart balloons at their forward ends. The balloons may be inflated to isolate a region in a blood vessel to allow localized introduction of thrombolytic agents. U.S. Pat. No. 4,631,052, describes a forward cutting catheter which may include a distal balloon (FIG. 9) to prevent release of emboli. Other forward cutting catheters are disclosed in U.S. Pat. Nos. 4,664,112 and 3,732,858. Percutaneous aspiration thromboembolectomy involves the removal of thrombus by aspiration into an open distal end of a catheter. The procedure is described in Starck et al. (1985) Radiology 156:61-66. U.S. Pat. No. 4,729,763, describes a front-end cutting catheter having a tubular auger bit which extends from the distal end of an outer catheter tube. U.S. Pat. No. 4,732,154, describes a front end cutting catheter where a tubular blade is advanced through thrombus over a guidewire having a helical coil thereon. U.S. Pat. No. 4,728,319, describes a front-end cutting catheter which mates with a distally located strainer cup and seal to prevent the release of emboli. U.S. patent application Ser. No. 128,770 (naming applicant herein as the sole inventor) describes a vascular catheter having a strainer at its distal end. The strainer is an expandable structure which utilizes a coaxial sheath for contraction. The strainer is intended to be disposed downstream of various angioplastic techniques to capture released emboli.